The present invention relates to an element arrangement board and an element arrangement method for arranging a plurality of elements at predetermined positions. More particularly, the present invention relates to an element arrangement board and an element arrangement method for arranging a plurality of elements in a self-aligning fashion using motion of the elements in fluid.
Conventionally, to arrange and assemble elements in a matrix to an image display apparatus, the elements are formed on a board as in a liquid crystal display (LCD) panel or a plasma display panel (PDP). Alternatively, independent LED packages are disposed on a board as in a light emitting diode (LED) display unit. A conventional image display apparatus such as an LCD or a PDP does not allow element isolation with regard to the pitch of elements or pixels. Therefore, elements are usually formed in a spaced relationship from each other by a pixel pitch of the image display apparatus from the beginning of the process of manufacture.
As one of the latest techniques, a method of arranging elements in a self-aligning fashion on a board has been proposed as a mounting method according to fluid self assembly. In the self-aligning fluid self assembly, a large number of elements after production are transmitted in a flow of liquid until they are received by holes formed on the surface of a film, and the film is transferred together with the elements to an apparatus on which the elements are to be mounted. The holes formed in the film are compatible with the elements to be mounted in terms of the shape. In this manner, the large number of elements are taken out in a state wherein they are retained on such a specific film as described above from the fluid and transferred to the apparatus.
Also another technique has been proposed, for example, in U.S. Pat. No. 5,783,856 (hereinafter referred to as Patent Document 1), Japanese Translation of PCT for Patent No. Hei 9-506742 (hereinafter referred to as Patent Document 2) or Japanese Patent Laid-Open No. Hei 9-120943 (hereinafter referred to as Patent Document 3). According to the technique, concave structures for receiving elements are formed on a mounting board on which the elements are to be arranged. Then, in a state wherein the mounting board is placed in the atmospheric air or in fluid, a plurality of semiconductor chips are dispersed so as to be disposed into the concaves in a self-aligning fashion.
The technique disclosed in Patent Documents 1 to 3 mentioned above is illustrated in FIG. 8. Referring to FIG. 8, a flat board 10 having holes 11 formed thereon is immersed in fluid 13. Then, elements 12 for display are thrown into the fluid 13 such that they move in and together with the fluid 13 so that they may be fitted into the holes 11 and mounted on the board 10. In element arrangement, since an element miss which is appearance of a hole 11 in which no element 12 is fitted signifies deterioration of the yield, it is necessary to supply the elements 12 into the holes 11 with certainty so that no such element miss may occur.
Where the board 10 is used directly in an image display apparatus or a like apparatus, the distance between the elements 12 is equal to the pixel pitch. This makes the size of the elements 12 small in comparison with the distance in arrangement between the elements 12. Consequently, the density in which the elements 12 are arranged on the board 10 is comparatively low, and the distance over which an element 12 reaches a hole 11 is long and also the time until an element 12 is fitted into a hole 11 is long accordingly. Thus, to fix the elements 12 with a high yield at the pixel positions at which the holes 11 each in the form of a hole are formed, it is necessary to continue the operation until the elements 12 are fitted into the holes 11 with certainty. Therefore, the technique described has a problem in that the time required before the elements 12 are fitted into all of the holes 11 is long and the throughput is low.
Therefore, to allow the elements 12 to be fitted with certainty into the holes 11 in a short period of time, it is necessary to supply an overwhelmingly greater number of elements 12 than the number of holes 11 formed on the board 10 as seen in FIG. 8. Although only some of the great number of elements 12 supplied on the board 10 are fitted into the holes 11, such supply of an overwhelmingly great number of elements 12 raises the probability that all of the holes 11 may be filled with the elements 12 in a short period of time. Therefore, the time required for mounting of the element 12 can be reduced and the mounting yield can be improved. However, where the size of the elements 12 is comparatively small with respect to the distance in arrangement of the elements 12, it is necessary to prepare and supply a number of elements 12 much greater number than the number of elements 12 to be arranged into the fluid. Therefore, the technique described above has a problem in that the required number of parts is great and a high production cost is required.